The present invention generally relates to a laser beam projection device and, in particular, to an arrangement for automatically leveling the device.
Laser light systems have been employed in numerous surveying and construction applications. In one such system, a laser light transmitting device provides a rotating laser beam which establishes a reference plane. In effect, the rotating laser beam is used to define a plane of light that acts as either a horizontal elevational reference or a sloped elevational reference, as desired, over an entire work area. The laser light is either detected by the naked eye or by one or more laser beam detectors, placed at considerable distances from the transmitting device. Various construction tasks may be performed based on visual perception of the laser light. Similarly, detectors may be used to intercept the rotating laser beam and determine a desired elevation and grade at selected points throughout the work area.
In the laser light transmitting device, the plane of light is produced by projecting the beam generally upward and then deflecting the beam ninety degrees within a pentaprism or pentamirror assembly. The pentaprism assembly is rotated about a vertical axis within the transmitting device to cause the beam to rotate, thereby defining the reference plane. The laser light transmitting device must be substantially level in order to function properly and to define the desired reference frame accurately. The beam of light which is projected upward will be substantially plumb with respect to the ground when the laser transmitting device is substantially level.
Prior art devices have included standard leveling vials attached to the housing of the laser light transmitting device to indicate to the transmitter operator that the transmitter is badly misaligned, and to permit manual adjustment of the transmitter to a more level position. Such leveling vials include a bubble suspended within a liquid medium, with the bubble position providing a rough indication of the degree of level of the housing. Leveling screws are included on the housing which may be adjusted by the operator to level the base. An automatic compensator may also be used to optically compensate for slight misalignments of the housing. The compensator includes a compensator cup which is suspended by thin wires within the housing, and a compensating lens in the cup, positioned in the path of the upwardly projected laser light. The compensator will automatically shift laterally so as to adjust the position of the laser beam so that it has a plumb orientation with respect to the ground as it emerges from the compensator. To function properly, the compensator must be within a certain degree of level, e.g. 12 minutes, in order to swing freely so as to have any effect on the orientation of the laser beam.
Such prior art devices are disadvantageous because the initial leveling of the base is dependent, in part, upon the skill of the operator. Manual leveling of the laser light transmitting device within 12 minutes is also tedious and time consuming for the operator. In addition, since the leveling operation is completed with respect to the base, the alignment between the housing and the compensator must be precise.
Other prior art systems include automatic leveling devices which attempt to level the laser light transmitting device based on a signal from an electronic leveling vial. The electronic leveling vials are similar to the standard leveling vials except the electronic leveling vials emit a signal representative of the relative position of the vial. The signal is then used to level the base of the laser light transmitting device to within 12 minutes so that the compensator may then adjust the position of the laser beam to a plumb orientation. Such systems are disadvantageous because the leveling activities are completed with respect to the base instead of the compensator. For accurate leveling so that the compensator is within 12 minutes of level, the alignment between the compensator and the housing must be precise.
Accordingly, there is a need for an accurate and automatic system for leveling a laser light transmitter which is independent of the alignment between the compensator and the housing.